The present invention relates to a process for drying synthetic resinous latexes utilizing a fluidizedbed. More particularly, the present invention relates to a method for preparing a polymeric blend stock, wherein one of the polymeric components is recovered in a dry form from a latex thereof by contacting droplets thereof with a fluidized bed of particles of the remaining polymeric component of the blend stock. The mixture thereafter may suitably be melted to achieve a desired polymeric blend. The present invention additionally embodies an apparatus suitable for the preparation of such a polymeric blend stock.
It is previously known to prepare thermoplastic resins by emulsion or suspension processes to thereby achieve a thermoplastic resinous product in a latex form. Suitable thermoplastic polymers include homopolymers and copolymers usefully employed as elastomeric impact modifiers, compatibilizers, or hard resinous components of polymeric blends. Previously, such latexes are dried to form a powder typically by a spray process. Although spray drying results in a suitable product for preparation of blends and eliminates a tendency of the latex to coagulate and stick into an intractable mass during the drying process, the process is difficult to operate in a commercial manner. Typically, a spray dryer requires expensive equipment which is subject to several serious shortcomings. Typically, a cyclone separator, a filter such as a bag house filter, and a final water scrubber are required to recover the spray dried product. Each of these components is subject to maintenance requirements and generates a certain amount of product loss. For example, filtration can result in losses of about 4 or 5 percent of the final product. In addition, periodic cleaning is often necessary to remove deposits from the equipment. Moreover, spray drying creates a very fine dust and the ever present danger of an explosion. Thus, spray drying equipment normally requires special handling precautions to avoid the generation of such dust and preferably the use of an inert atmosphere, thereby adding to the expense and complexity of the spray drying process.
When used ultimately in the preparation of a polymeric blend, the fine powdery polymeric product resulting from drying of a latex creates further handling problems. Besides the ever present dust, necessitating special handling procedures to prevent the dust from entering the atmosphere, clumping or settling of the finely particulated dried latex can result in uneven melt blending of the resulting polymer blend and ultimately variations in the composition of the resulting polymeric blend. Moreover, generation of the ultimate blend requires careful metering of the polymeric ingredients in a separate process operation.
It would be desirable to provide a process for drying a latex of a thermoplastic polymer which avoids sticking or coagulation of the dried latex as well as the problems created by spray drying of finely particulated polymer products.
It would also be desirable to provide a process for preparing a polymeric blend stock providing greater control over the uniformity thereof and eliminating dust handling problems.
In addition it would be desirable to provide a process for preparing polymeric blend stocks in a simple and expeditious manner.
Finally, it would be desirable to produce a polymeric blendstock comprising particles comprising an inner region of a first polymer and a second region comprising a different polymer or mixture thereof disposed on the outer surface of the first polymeric region.